1. Field of the Invention
This invention relates to a combined pressure relief and pressure indicating mechanism, and more particularly, to such a mechanism usable with a sealed housing filled with a fluid at super-atmospheric pressure. Specifically, the present invention relates to a combined pressure relief and visible pressure indicating mechanism for the housing of a high-voltage, circuit interrupting device which is filled with a dielectric arc-extinguishing gas at super-atmospheric pressure.
2. Background of the Invention
Many types of high-voltage circuit interrupting devices include porcelain housings containing an arc-extinguishing fluid, often a gas, at super-atmospheric pressure; i.e., a pressure greater than one atmosphere. The circuit is interrupted by separating normally engaged contacts within the housing, while an arc or arcs are drawn therebetween. The arcs are subsequently extinguished by elongation thereof and the action of the gas. Under certain conditions, increased gas pressure within the housing may fracture the housing, unless provision is made for rapidly relieving the excess pressure. Moreover, under certain other conditions, the pressure of the gas within the housing may drop to a level at which the ability of the interrupting device to extinguish the arcs is severely reduced or eliminated. Examples of circuit interrupting devices which include porcelain housings containing arc-extinguishing gases under super-atmospheric pressure are found in a co-pending, commonly-assigned U.S. patent application Ser. No. 930,774, filed Aug. 3, 1978 in the names of Opfer and Vojta, and in the following commonly-assigned U.S. Pat. Nos. 3,039,481; 3,077,527; 3,163,736; 3,229,848; 3,508,022; and 3,769,477.
The above-referred to U.S. Pat. No. 3,229,848 also discloses and claims a pressure relief means which provides for the rapid venting of the procelain housing of the circuit interrupting device. The pressure relief means therein disclosed and claimed operates very well and has found wide use. The interrupting device of such patent, however, employs a separate, low pressure indicating means and as a consequence, both a pressure relief means and a low pressure indicating means must be provided therefor. It would be convenient, efficient and economical to provide a combined pressure relief and pressure indicating mechanism which performs both functions with a single unit and which is reliable and not subject to deterioration.